Swing-tongue harvesters have become extremely popular over the years due in part to their ability to be quickly and easily maneuvered from the tractor seat around obstacles, through right angle turns, and otherwise operated in a manner previously reserved only for self-propelled vehicles. In the case of "center-pivot" swing-tongue harvesters in which the tongue is pivoted at or near the transverse center of the machine, the machine is capable of being used to cut back and forth across a field in subsequent passes as it is shifted first to the right during one pass and then out to the left on the return pass.
Having a pulling tongue which is shifted between relatively sharp angular positions, however, creates problems in the delivery of driving power from the tractor to operating components of the machine. One way to accomplish such power delivery is through the use of a remote hydraulic motor back on the machine which is coupled with the tractor hydraulics in such a way that hydraulic power is supplied to the motor through long flexible lines leading from the tractor back to the motor. By positioning the hydraulic motor back on the harvester itself, there is no need to have mechanical drive lines extending between the tractor and the harvester which would become subjected to the ongoing angular movements and turns between the harvester and the tractor. The hydraulic hoses can instead flex to the extent necessary to accomplish such angulations, and it is only necessary to have a mechanical drive line system leading from the hydraulic motor down to the components to be driven.
However, a hydraulic drive system of this type is expensive and has certain power limitations, as well as other problems. Therefore, it would still be desirable, if possible, to have a mechanical drive line between the tractor and the harvester which could supply all of the power needs of the harvester and yet fully withstand the twists and turns and angular motions effected by the harvester as it is used and maneuvered in its most efficient manner.